New Rat Model ofPneumocystisPneumonia Induced by Anti-CD4⁺T-Lymphocyte Antibodies

Abstract

The CD4؉ T lymphocyte plays a central role in host defense against Pneumocystis pneumonia but has received only limited attention in rats. CD4؉ T-cell-depleting (OX-38) and nondepleting (W3/25) monoclonal antibodies, which recognize an identical or adjacent epitope, were administered for up to 14 weeks to Lewis rats that had been exposed to Pneumocystis. While OX-38 produced a greater decrease in circulating CD4؉ cells than W3/25, both antibody treatments resulted in similar effects on the health of the rats and the levels of Pneumocystis pneumonia, which were milder than those found with corticosteroids. W3/25 also did not enhance the severity of Pneumocystis pneumonia achieved with corticosteroids alone. We conclude that CD4 ؉ cell function is more important than CD4؉ cell number in host defense against Pneumocystis in the rat and that this new model permits study of opportunistic infections in the rat without the confounding effects of corticosteroids.Pneumocystis is an extracellular fungus of low virulence that causes pneumonia in immunocompromised individuals, such as human immunodeficiency virus-positive patients and cancer and organ transplant patients. Various immunodeficient and immunosuppressed rat and mouse models have been used to study the interaction between Pneumocystis and host (9,11,31,32). The corticosteroid (CS)-treated rat is the original animal model used to study Pneumocystis pneumonia and is the source of most available information on the epidemiology, immunopathogenesis, diagnosis, and therapy of the disease (3, 9). However, this model is limited by the broad immunosuppressive effects of steroids on the immune system, including lymphocyte depletion and impairment of function, reduced leukocyte chemotaxis and phagocytosis, and deficient antibody (Ab) production (38).Clinical and experimental studies have shown that CD4 ϩ T lymphocytes play a central role in host defenses against Pneumocystis (14,25,29,37). Pneumocystis pneumonia can be induced in mice exposed to the organism by the administration of GK1.5, a rat immunoglobulin G2b (IgG2b) monoclonal antibody (MAb) specific for CD4 ϩ cells (31). This model has proven to be popular because it circumvents the need for CS immunosuppression; however, no such model exists in rats. Given the increasing evidence of the genetic diversity and host specificity of Pneumocystis (6, 33), it cannot be assumed that the results obtained in one animal species can be applied to another. The development of a CD4 ϩ depletion model in the rat would be important in studying the role of CD4 ϩ T cells in the rat.MAbs have been produced to rat CD4 ϩ cells, and their properties have been analyzed by in vitro or short-term in vivo studies (2,5,26,39). These Abs are of two general types: depleting Abs, which trigger cell lysis; and nondepleting Abs, which cause downregulation of CD4 antigen expression resulting in inadequate T-cell receptor (TCR)-antigen-major histocompatibility complex class II interaction (34). These Abs have been used in a variety of autoimmune or ...

Sensitized Splenocytes Result in Deleterious Cytokine Cascade and Hyperinflammatory Response in Rats withPneumocystisPneumonia despite the Presence of Corticosteroids

“…Donor spleen cells were suspended in 96-well plates at 1.0 ϫ 10 5 splenocytes/well and cultured for 4 days in the presence of MSG (6.0 g/well), ConA (1.0 g/well; Sigma) as a positive control for proliferation, or RPMI, as previously described (35). After incubation at 37°C and 5% CO 2 for 4 days, the cultures were pulsed with 1.0 Ci of [ 3 H]thymidine/well (20 Ci/mmol; New England Nuclear, Boston, Mass.)…”

“…Untreated donor rats exposed to Pneumocystis pneumonia rats were sacrificed by an overdose of CO 2 (30), and the spleens were excised. Lymphocytes were obtained from the spleens by homogenization using a Tenbroeck tissue grinder (Wheaton, Millvill, N.J.) and filtered through a 0.4-mm-pore-size cell strainer, and the red blood cells were lysed with 0.85 M ammonium chloride, as described previously (35). The splenocytes were washed and suspended in RPMI, and MSG was added (final cell concentration, 10 6 /ml; final MSG concentration, 50.0 g/ml).…”

“…Rodent models have proven to be useful in studying the dual effects of the host immune response to Pneumocystis and the role of CD4 ϩ and other cells in this response (2,11,13,14,17,35,39). One experimental approach has involved the adoptive transfer of immune splenocytes or purified T-cell populations into athymic (nude) or severe-combined-immunodeficiency (SCID) mice with Pneumocystis pneumonia.…”

Innate and adaptive antifungal immune responses: partners on an equal footing

“…(Table 3). For example, depletion of CD4 + T cells results in increased susceptibility to Pneumocystis pneumonia infections in rodents 33 . Increased numbers of circulating CD4 + and CD8 + memory T cells are detectable in P. brasiliensis ‐infected cancer patients 34 .…”

New Insights in Medical Mycology

“…Depletion of CD4 + T cells results in increased susceptibility to P. pneumonia and other mycotic infections both in mice (Shellito et al, 1990) and rats (Thullen et al, 2003). Differentiation of naive Th into Th1 or Th2 type represents a major determinant of resistance or susceptibility of the host to fungal infections (Shoham & Levitz, 2005).…”